The diverse electronic technologies that are currently used to amplify and record professional performances on musical instruments suffer from a variety of critical deficiencies. The most problematic deficiencies concern noise ingress, internally generated noise, nonlinear amplitude response, audio dynamic range, frequency response and audio time latency, all of which affect the quality and fidelity of the music. This is especially a challenge for processing sound from stringed instruments, as discussed below. However, many of the same deleterious electronic phenomena affect other types of instruments as well.
Noise ingress arises in stringed instruments when electrically powered equipment radiates an un-programmed radiofrequency or even audio-range signals as a result of electromagnetic fields that are an incidental and unwanted byproduct of their circuit designs. The resulting ambient signals are received by the electronic audio pickup components in the instruments, and compromise their output. The problem has been universal because electronic equipment is ubiquitously and prolifically present in musical performance environments, and because electronic shielding to prevent such emanations is often absent or grossly inadequate. The issue is further complicated by a much older phenomenon in purely acoustic instruments wherein ambient noise in the audible range enters a harmonic cavity and echoes there, such as in a wind instrument, stringed instrument or percussion instrument.
Externally generated signals are not the only source of noise. The instruments may have undesirable resonances, and the instruments' own complement of in-line electronics can also contribute. There such noise is generated internally and is then layered undesirably onto the desired audio sound. Linear audio equipment in particular is a source of this.
In addition to noise, other artifacts arise from intrinsically flawed sound engineering hardware, causing distortion of the sound. In particular, nonlinear amplitude responses are inherent in the analog amplification elements that are widely used in present art electronic amplification devices. In this case amplification from the devices does not scale proportionally with the magnitude of an instrument's actual amplitude output. Thus non linear elements introduce signal components that do not emanate from the instrument.
Nonlinear scale changes for volume have a parallel in truncation of the dynamic sound range. The dynamic range refers to the extent of difference between the loudest possible sounds and quietest possible sounds conveyed in the output: larger ranges permit more nuanced expression in the music. To date the dynamic range of analog audio signals that can be handled electronically has been limited, because as the voltage of a sound control component approaches that of the power supply, thermal noise and analog signal compression become substantial. Vacuum tubes are currently in favor to improve the feasibly attainable dynamic range, but these have their own disadvantages: limited availability, limited mobility, and very high voltage requirements.
Just as the dynamic sound range is often truncated, audio apparatus often attenuate or overemphasize certain frequency bands relative to other frequency ranges. The audio frequency response quantifies the electronic ability to reproduce relative amplitudes (as measured from input to output) uniformly across a frequency spectrum. The inhomogeneous propagation of magnitudes across frequency spectra may be accompanied by phase changes (measured in radians) in the analog signal, which also differ depending on the frequency, again distorting the sound. These flaws are common in electronic amplification, microphones and loudspeakers, and phase shifts commonly arise from capacitive reactance or inductive reactance in their components.
Some hardware-derived artifacts occur along an additional dimension: they introduce unintended delays in the processing and transmittal time during which sound is delivered through the circuit. Audio latency is the duration between the time an instrumental sound is made and the time when it actually leaves the speaker. Latencies within a certain range have been proven to be disorienting to the human brain. Research studies have also shown that the perception of optimal latency levels varies between individuals. (See Michael Lester and Jon Boley, “The Effects of Latency on Live Sound Monitoring”, Audio Engineering Society Convention Paper 7198, Presented at the 123rd Convention 2007 (October 5-8), New York, N.Y.) It is counterintuitive, and in some cases impossible, yet zero time is not always the ideal for perceived optimal latency. Thus the latency level must be taken to a middle ground that satisfies the most listeners. Sources of latency increases include analog-to-digital conversion, buffering, digital signal processing, transmission time, digital-to-analog conversion and the speed of sound.
In order to minimize these various effects, the current state of the art links stringed instruments to electronic audio equipment by means of wire cables. This has been a very imperfect solution. The cables hamper musicians' freedom of motion, are subject to electrical noise interference, have a high initial cost and must be replaced frequently. Moreover even use of cables has not been able to circumvent the above problems entirely. Wireless connections have been used as an alternative, but they require frequency modulation that is subject to radiofrequency interference and noise, and for recording sessions their bandwidth and dynamic range may be limited.
Thus there is an ongoing need for improved methods and devices to process musical performance with high fidelity.